Urban Tree Canopy Study

The City of Atlanta contracted researchers at the Center for Geographic Information Systems (CGIS) and the Center for Quality Growth and Regional Development (CQGRD) at Georgia Tech to quantify the existing Urban Tree Canopy in the City. Urban Tree Canopy (UTC) is defined as the layer of leaves, branches and stems of trees that cover the ground when viewed from above. The aim of the Atlanta UTC study is to help City decision makers and stakeholders better understand and manage their forest resources.

Why Urban Trees and Forests Are Important?

The urban forest — defined as the system of trees and other plants that grow individually, in small groups, or under forest conditions on public and private lands in cities, suburbs, and towns — is part of the larger ecological system, and it provides many of the same benefits as natural forest systems. Current estimates indicate that 80% of the US population lives in urban areas. As more rural land becomes urbanized, the role of urban forests and urban tree canopy becomes increasingly important. Urban trees provide a number of established aesthetic and environmental benefits.

Trees clean particulates from the air and soil, which helps decrease air and water pollution.

Trees provide a stormwater management service by intercepting rainfall that would otherwise flow directly into water bodies and the drainage system, causing streambank erosion, and potentially overwhelming the stormwater system, especially in areas with combined storm and sanitary sewers.

Trees provide habitat for native pollinators, migrating birds, and other important wildlife.

Trees make neighborhoods and urban areas more livable by providing aesthetic, social, and psychological benefits for residents.
For many residents and visitors, Atlanta’s mature and vibrant urban tree canopy is its signature environmental feature.

Project at a Glance

The City of Atlanta contracted researchers at the Center for Geographic Information Systems (CGIS) and the Center for Quality Growth and Regional Development (CQGRD) at Georgia Tech to quantify the existing Urban Tree Canopy in the City. Urban Tree Canopy (UTC) is defined as the layer of leaves, branches and stems of trees that cover the ground when viewed from above.

The aim of the Atlanta UTC study is to help City decision-makers and stakeholders better understand and manage their forest resources. Specific goals for this assessment were to (1) map urban tree canopy and other land cover across the City; (2) quantify tree cover for various geographies within the city (neighborhoods, NPUs, council districts, parks, zoning and land use, watersheds, stream buffers); (3) establish a baseline for measuring canopy change over time; (4) identify planting sites; and (5) summarize and make recommendations based on findings.

The research team identified and measured the existing tree canopy in the City of Atlanta through the analysis of high resolution, multi-spectral, “leaf-on” Quickbird satellite imagery obtained by the city in October 2008 from Digital Globe Inc. The analysis was accomplished utilizing both established and newly developed land cover classification techniques. The project team also developed coverage area data for two other general land classes: non-tree vegetation, and non-vegetation. Accuracy assessments were conducted to validate findings.

Summary of Findings

The research team estimates that in October 2008, 47.9% (40,524 acres) of the land within the city limits was covered by urban tree canopy (UTC), 22.1% (18,722 acres) was covered by non-tree vegetation (NTV) such as grass, shrubs, and other plants; and 30.0% (25,386 acres) was covered by non-vegetation (NV) such as paved surfaces and buildings.

Urban Tree Canopy in Atlanta

Urban tree canopy coverage varies significantly across Atlanta and is strongly related to zoning and land use, with the highest concentration of existing urban tree canopy located on residential property and the lowest in the downtown area and along transportation corridors. Significant concentrations of tree cover are also found along some of Atlanta’s stream corridors. The accompanying graphics show the extent and distribution of canopy across the City of Atlanta.

Canopy Distribution Across the City

The majority of tree canopy within Atlanta’s city limits (77%- 31,194 acres) is on single-family residential land. Single-family land makes up 60.8% of the city’s total land area.

Multi-family residential land contains the second highest amount of the city’s total canopy (8%), followed by industrial (6%); these categories make up 9.4 % and 11.8% of the city’s total land area, respectively.

Parks contain approximately 4.9% (2,070 acres) of the city’s total tree canopy; park land makes up 4.5% of the city’s total area.

Canopy Concentration within Selected Geographies

61% of all single-family residential land is tree covered.

40% of all multi-family residential land is tree covered.

20% of all land zoned commercial is tree covered.

Densely developed areas, such as downtown, surrounding neighborhoods, and former Atlanta Housing Authority developments have less than 5% tree cover.

Several neighborhoods in the north and southwest have more than 70% canopy coverage, particularly those along Nancy Creek and Utoy Creek.

Among parks over 50 acres in size, canopy coverage ranges from a low of 18% at Lakewood to a high of 94% at Cascade Springs Nature Preserve.

Canopy coverage for sub-watersheds ranges from a low of 18% in Proctor Creek to a high of 72% in Long Island Creek — canopy in 100 foot stream buffers ranges from a high of 80% along North Utoy Creek to a low of 35% along Intrenchment Creek, with a City-wide average of 65% canopy coverage within 100-ft. stream buffers.

How Does Atlanta Compare To Other Cities

At 47.9 %, Atlanta has the highest percentage of overall urban tree canopy in the nation when compared to other cities that have conducted UTC Assessments. While many variables affect the presence of tree canopy – ranging from geography and climate to development patterns, tree protection and planting policies – at the turn of the 21st century, Atlanta remains a “City in the Forest.”

Trees provide shade, clean the air, and reduce storm water runoff. Trees improve our quality of life and give us beauty, food, and habitat for wildlife and pollinators. Every day, this important resource — our urban forest — is increasingly under threat. As residents, voters, and environmental stewards, we want Atlanta’s elected officials and community leaders to know that we all care about the trees in our city.

Recommendations

The results of the Georgia Tech Urban Tree Canopy Assessment will benefit the City of Atlanta in multiple ways. The City can immediately use the findings to:

Refine policies and set canopy goals to ensure that each area of the City receives the benefits of a healthy canopy and that the overall tree canopy is maintained and increased over time.

Establish baseline tree cover information from which the City can measure and track progress.

Establish an Urban Forestry Master Plan for achieving canopy goals.

Educate the public about tree canopy in Atlanta through an online, interactive map accessible from the City’s website.

Streamline the identification of potential planting locations based on derived ratios of UTC to Non-Tree Vegetation. Inform sustainability efforts and policy decisions related to climate, water and air quality, tree preservation and watershed protection.

Establish a methodology to ensure comparability against results from future UTC studies.
The data generated by this research project will serve as a guide to Atlanta’s policy makers, a resource for its citizens, and a tool for planners and others concerned about Atlanta’s urban forest.

1. Magnolia Collection

Magnolias are part of an ancient lineage of flowering plants dating back approximately 95 million years. The Atlanta BeltLine Arboretum is home to 18 types of magnolias from evergreen to flowering. Two magnolias in particular have witnessed history as they were planted just beyond the outfield wall for the former Ponce de Leon Park, where the Atlanta Crackers played baseball. Babe Ruth and Eddie Matthews both hit home runs that were caught in the canopy of one of these magnolia trees. As part of Arboretum experimentation, we have taken cuttings from these historic magnolias and grown them into new trees so that this piece of history can live on the Atlanta BeltLine Arboretum and in new parks and baseball fields around Atlanta.

2. 33 Oaks

The oak trees on this slope and throughout the Arboretum represent many ecosystems in Georgia, from bottomland hardwood swamps to granite outcrops. Of the approximately 90 species of oaks native to the United States, 33 are native to Georgia. All 33 oaks are growing on this slope and between them dance 33 stainless steel leaf sculptures – one for each tree.

These metal oaks were designed and crafted by David Landis of Landis Sculpture Studio. Learn more about David’s work here.

3. Beech Circle

Among the stateliest of our native trees, beeches are indicative of a mature forest. Though they can take around 40 years to produce a large quantity of nuts, beech trees are critical for wildlife. Beeches provide food and shelter for all kinds of birds and mammals, such as the red-headed woodpecker. Dubbed the fairy ring, the circle of beech trees here surrounds a granite outdoor classroom and gathering place where you can contemplate how the beech trees will look in 3, 5, and 10 years!

4. Eastside Azalea Collection

Despite the native azalea holding the title of Georgia’s State Wildflower, it is underused in the landscape. The Atlanta BeltLine Arboretum is now home to the largest public native azalea collection in the Atlanta Area with over 300 azaleas on display. The collection highlights over 25 species, cultivars, and varieties, and is home to all 13 azaleas native to the state of Georgia. This collection focuses on named cultivars (varieties that have been selected for depending on color, size, bloom time, etc.) within two series called the Georgia Moon Series and the Sunrise to Sunset Series. The Georgia Moon Series will have fragrant white-blooming Georgia native species, and the Sunrise to Sunset Series will be comprised of Georgia native species in warm orange, reds, and soft yellows blooming from March – July.

5. Stumpery Garden

This stumpery garden will be a horticultural oddity, serving as a public place for learning and exploration and demonstrating how trees can be utilized in a beautiful way. Stumpery gardens utilize dead, fallen, and storm-damaged trees as an asset to the garden – providing critical habitat for beetles, frogs, birds, and small mammals such as chipmunks. Whole logs are placed upside down to display their root structure, and logs, branches, and pieces of bark are arranged to form walls and archways. Plants such as ferns, lichen, mosses, soft grasses, and trailing plants are encouraged to grow on and around them.

6. Westside Azalea Collection

Different from the Eastside collection, the Westside collection has all straight species and natural varieties that encourage free hybridization. These azaleas are all grown from seed so there are many variations in the hues even between the same species.

7. Persimmon Woods

Home to the largest American persimmon tree in the state of Georgia, this remnant old growth forest on 1.3 acres provides habitat to a variety of deep forest flora. Walking through a nature trail and over a few bridges will bring you up close and personal with woodland groundcovers, rare spring ephemerals (plants with a short life cycle) such as trillium, and a large collection of native woody species. Enjoy the seasonal blooms, learn from plant identification signs, and get hands-on with volunteer opportunities to plant, divide woodland perennials, and collect seed.